Zac Vawter, 31, is to put the revolutionary prosthetic to the test on Sunday, when he attempts to climb 103 flights of stairs to the top of Chicago’s Willis Tower.

The whirring, robotic leg will respond to electrical impulses from muscles in his hamstring, with Mr Vawter’s thoughts triggering motors, belts and chains to synchronise the movements of the prosthetic ankle and knee.

Mr Vawter hoped to reach the top of the tower in an hour – longer than he would have taken before his amputation, but in less time than it would take him to use his normal prosthetic leg.